[LangRef] Clarify absence of rounding guarantees for fmuladd.
[LangRef] Clarify absence of rounding guarantees for fmuladd.

During the review of D67434, it was recommended to make fmuladd's
behavior more explicit. D67434 depends on this interpretation.

Reviewers: efriedma, jfb, reames, scanon, lebedev.ri, spatel

Reviewed By: spatel

Differential Revision: https://reviews.llvm.org/D67552

git-svn-id: 0ff597fd157e6f4fc38580e8d64ab130330d2411@372892 91177308-0d34-0410-b5e6-96231b3b80d8

llvm-mirror/llvm,GPUOpen-Drivers/llvm,llvm-mirror/llvm,llvm-mirror/llvm,llvm-mirror/llvm,llvm-mirror/llvm,llvm-mirror/llvm,GPUOpen-Drivers/llvm,GPUOpen-Drivers/llvm,GPUOpen-Drivers/llvm,GPUOpen-Drivers/llvm,llvm-mirror/llvm,llvm-mirror/llvm,llvm-mirror/llvm,GPUOpen-Drivers/llvm,GPUOpen-Drivers/llvm,GPUOpen-Drivers/llvm